thanks palms

Karl's brush looks promising. I thought of one way of making it more realistic:
Apply all stars on a blank layer ,
Duplicate this layer and apply guassian blur on it.
Reduce the opacity of the duplicate layer on top until it shows soft edges around the stars. I am yet to try out though
The other random thought is to find a really realistic star burst in a real photo and extract it using mask or extraction in CS2. Then soften the edges and make it to as a customer brush.